Re: [ATM] Eyepiece questions?

[Woodchuck <djv@bedford.net>]

On Tue, 12 Oct 2004, Jim Miller wrote:

> I'm trying to make something that would fit in a 1.25" eyepiece holder. It
> has to be metal for shielding reasons so I'm researching eyepiece
> construction and looking to avoid buying a lathe...

Heh.  This is hard (avoiding a lathe for eyepiece fun).  The 7"
mini-lathes from the Chicoms are probably good for this, and you
might even find a used one.  New, they're around 500USD, probably
more than you want to spend.  More than I want to spend, too.  I
think what you want to do is to borrow a little time on somebody
else's lathe, this can sometimes be done at a junior college, or
in the more backward areas of the country where "manual arts" are
still taught, the high skool or votech.

There was an article, my flakey memory seems to scream that it was
written by someone named Ferson, in the old, original ATM series from
Scientific American about eyepiece construction without a lathe, and
showed numerous kludges.  They depend on skillful hand work.

For tubing see
"http://www.onlinemetals.com/merchant.cfm?pid=1560&step=4&showunits=inches";,
they have 1.25 x 0.062 wall brass at about ten bucksUS a foot,
probably also other metals if you want stainless.  But brass is
"traditional", and there's no ~compelling~ reason to plate it.  It
can be nice to blacken it chemically, however.  1.25 is a sort-of
non-standard size, the usual series goes by 1/2" in this region.

Another possible source would be bronze bushings, which are made
to a variety of sizes, and might be available at hardware or auto
stores.  They are certainly available at industrial supply outlets
like McMaster-Carr.  (www.mcmaster.com).  These can be had with
rather thick walls, and their dimensions are reliable.  Problem is
that some are oil-impregnated, but some are not.  Some have collars
on them already, a plus.  (Called "flanged bearings").  If you live
in an industrial area, there will be a "bearing supply" store nearby.

See www.mcmaster.com.  On the home page, scroll down to "Power
transmission" on the right frame, click on "plain bearings".  ID
1", OD 1.25, length 3 inches, will run around $5.  $5 is kind of a
small order for these boys, although they have no minimum... they
sell "everything" mechanical.  (Also tubing, min order 3 feet, page
114).

> First: Anyone know of a standard for 1.25" eyepiece OD dimensions? Is the
> spec 1.25"+/- something?
>
> Second: Are eyepiece barrels typically brass with some sort of plating?

In the olden days, yes.  Brass is your friend...

> Salvaging a cheap eyepiece for a easily solderable brass fitting would be
> nice.

Dave

_______________________________________________
ATM mailing list http://www.atmlist.net/